Number guess on an Arduino Uno

// Number guess: the board thinks of a number, you type it on a phone keypad.
//
//   pins 12, 11, 10, 9     keypad rows R1 to R4
//   pins 8, 7, 6           keypad columns C1 to C3
//   A0  LCD RS             A1  LCD E
//   A2, A3, A4, A5         LCD D4 to D7   (RW and V0 to GND)
//
// The pad is the twelve-key one off a telephone:
//
//     1  2  3
//     4  5  6
//     7  8  9
//     *  0  #
//
// Type a number between 1 and 100 and press `#` to send it. The display says
// HIGHER or LOWER, and `*` rubs out what you have typed. Get it right and it
// tells you how many goes it took and thinks of another.
//
// # Where the number comes from
//
// A board has no dice and no clock that is different on each run, so seeding
// the generator in `setup()` gives the same "random" number every time, which
// is the classic bug in every guessing game written on a microcontroller. This
// one seeds from `micros()` at the moment the first key of the game is pressed.
// That reading is a person's reaction time in microseconds, and nothing on the
// board can predict it.
//
// # Reading the pad
//
// Twelve keys on seven pins and no chip: each key shorts its row to its column,
// so the sketch scans: one row driven low at a time, the three columns read
// with their pull-ups on. mokxi_keypad.h does the scan and the debounce and
// hands back one character per press. It never drives a row high, because two
// keys held in one column would put one driven output across another.

#include "mokxi_keypad.h"
#include "mokxi_lcd1602.h"

const uint8_t ROWS[4] = {12, 11, 10, 9};
const uint8_t COLS[3] = {8, 7, 6};

Keypad4x3 pad(ROWS, COLS);
Lcd1602 lcd(A0, A1, A2, A3, A4, A5);

const int LOWEST = 1;
const int HIGHEST = 100;

int secret = 0;
int entry = 0;
int tries = 0;
bool seeded = false;

static void newGame()
{
  secret = (int)random(LOWEST, HIGHEST + 1);
  entry = 0;
  tries = 0;
}

static void showEntry(const char *note)
{
  lcd.setCursor(0, 0);
  lcd.print(note);
  lcd.padLine();
  lcd.setCursor(0, 1);
  lcd.print("Guess: ");
  if (entry > 0) {
    lcd.print(entry);
  } else {
    lcd.write('_');
  }
  lcd.padLine();
}

void setup()
{
  pad.begin();
  lcd.begin();
  lcd.print("Number guess");
  lcd.setCursor(0, 1);
  lcd.print("1 to 100, # ends");
}

void loop()
{
  char key = pad.pressed();
  if (key == 0) {
    return;
  }

  // The first press of the session is what the generator is seeded from: a
  // person's reaction time, which nothing on the board can work out for itself.
  if (!seeded) {
    randomSeed(micros());
    seeded = true;
    newGame();
    showEntry("Think of a go");
  }

  if (key == '*') {
    entry = 0;
    showEntry("Cleared");
    return;
  }

  if (key >= '0' && key <= '9') {
    if (entry < 100) {
      entry = entry * 10 + (key - '0');
    }
    showEntry("Typing");
    return;
  }

  if (key != '#') {
    return;
  }

  if (entry < LOWEST || entry > HIGHEST) {
    entry = 0;
    showEntry("1 to 100 only");
    return;
  }

  tries++;
  if (entry < secret) {
    entry = 0;
    showEntry("HIGHER");
    return;
  }
  if (entry > secret) {
    entry = 0;
    showEntry("LOWER");
    return;
  }

  lcd.setCursor(0, 0);
  lcd.print("Got it: ");
  lcd.print(secret);
  lcd.padLine();
  lcd.setCursor(0, 1);
  lcd.print(tries);
  lcd.print(tries == 1 ? " go. Again..." : " goes. Again...");
  lcd.padLine();
  delay(2000);
  newGame();
  showEntry("New number");
}